1. Field of the Invention
This invention relates to an engine for models having an electronic controlled fuel injection system.
2. Description of Related Art
FIG. 6 shows the structure of a conventional four-cycle glow engine which has been known as an engine for models. Exhaust gas discharged from an exhaust muffler 101 of the engine 100 is partially guided into a fuel tank 102 in order to pressurize fuel in the fuel tank 102. Fuel which is pressurized at an approximately constant pressure by means of exhaust gas is sent to a needle valve 103, and supplied to the engine 100.
According to the engine for models described herein above, engine operation under low rotation speed such as idling operation is unstable, and when the engine is accelerated rapidly from the low rotation condition, a lot of air is fed in the valve body, but the supply of fuel can not follow the supply of air, and the balance of air-fuel ratio is unbalanced. The rotation of the engine increases not smoothly and increases slowly, and can be stopped in the bad case. As a whole, the response is not good, the transition from the low rotation speed to high rotation speed or the higher rotation speed to low rotation speed requires a long time, it is a disadvantage of the conventional engines.
The inventors of the present invention proposed an engine to solve the above-mentioned problem in which a constant pressure was applied to fuel in a fuel tank, and the pressurized fuel was injected into a combustion chamber using an electronic controlled fuel injection system. The fuel injection system used for the engine for models comprises a box to which pressurized fuel is fed, a coil accommodated in the box, and a valve disposed movably in the coil for closing a fuel injection orifice with pressing force of a forcing means. A current supply to the coil of the fuel injection system actuates the valve body to move in the opposite direction against the pressing force, and the closed fuel injection orifice is opened to inject fuel stored in the box into the outside.
In the above-mentioned engine for models proposed by the inventors of the present invention, fuel consumption per one cycle is different depending on the rotation speed, it is required to inject more fuel into combustion chambers in order to increase the rotation speed. In detail, as shown in FIG. 7, the rotation speed of the engine is proportional to the fuel injection time, for example, the fuel injection time during low speed operation such as 2000 rpm is assumed to be 1, then the fuel injection time during high speed operation such as 8000 to 10000 rpm range is about 2.
In the above-mentioned engine for models proposed by the inventors of the present invention, because the pressure applied to fuel is constant, it is required to extend a single fuel injection time in order to increase the fuel supply that is injected with a single injection. Therefore, the current supply time supplied to the coil of the fuel injection system is extended with increasing in rotation speed, and the extended current supply time results in the increased power consumption, this is a problem. Further, in the method that the fuel supply is controlled by controlling the injection time for injecting pressurized fuel at a constant pressure, the injection time can be longer than the time of one cycle for high speed rotation, in such high rotation speed operation, the fuel supply can not be controlled, it is another problem.
It is the object of the present invention to provide an engine for models with low power consumption of an electronic controlled fuel injection system, which is capable of supplying fuel adequately to the operated rotation speed and capable of being operated stably in wide rotation speed range.